While the phenomenon of tip vortices has been recognized by aircraft designers for a very long period of time, such as at least 50 or 60 years, and a variety of devices for controlling or minimizing same have been proposed from time to time over a substantial portion of such period, the problem has in the past been considered one which was not capable of an economically acceptable solution and hence a problem to be tolerated. This has become particularly serious in more recent years, since the advent of large aircraft such as the Boeing 747, in that wing tip vortices of dangerous magnitude have been known from the initial appearance of such aircraft to extend for several miles behind them and to be of such magnitude as to cause severe adverse effects upon following aircraft. In some instances, aircraft as large as the Boeing 737 have been known to experience roll of as much as 90.degree. when caught in the wing tip vortex three or four miles behind a Boeing 747. While this has presented no great problem in the airways as such, in view of the spacing normally maintained anyway between aircraft therein, it has for several years been a serious problem in the maneuvering of aircraft at or near airports. For example, it is known that the ground controllers and air traffic controllers at a major airport can handle aircraft following one behind the other at a spacing of as close as two miles. However, because of the wing tip vortices generated by large aircraft, particularly such aircraft as the Boeing 747, it is normally necessary to space an aircraft following a 747 by as much as a minimum of five and one-half miles behind said 747 and often more than that to avoid the adverse effects of the wing tip vortices as above-mentioned. For smaller aircraft, such as Boeing 727's or 737's, or even for DC 10's, the spacing does not need to be as great, but it still often needs to be greater than would be required by the control capacity of the ground control and air traffic control personnel. Thus, because of such wing tip vortices, it is not possible to space aircraft either incoming or outgoing from an airport as close together as it would otherwise be possible, and the hourly capacity of an airport for receiving aircraft to, and directing aircraft from, a ground position has been severely restricted. Thus, the problem has long been recognized as serious but same has defied a commercially acceptable solution.
The prior art is replete with efforts to meet this problem, some of such efforts extending back for many years. Some workers in the field have attempted to generate counter-vortices in the hope that such would at least diminish the intensity of the undesired vortices (U.S. Pat. No. 2,477,461). Other workers in the field have attempted to discharge jets of air into the central zone of the vortex in order to dissipate the intensity thereof (U.S. Pat. No. 3,841,587). Still others have positioned fixed plates adjacent the tip of the wing, said plates being positioned substantially perpendicular to the plane of the wing and parallel to the direction of travel of the aircraft which affects the flow of air across the wing surfaces in such a manner as to diminish the intensity of the vortices (U.S. Pat. No. 3,845,918 and No. 2,120,760).
A very recent study of this phenomenon was published in May 1975 by Aeronautical Research Association of Princeton, Inc., Princeton, New Jersey, under the title of "Vortex Wakes of Conventional Aircraft". This study included a review of previously known methods of accomplishing the destruction or minimizing of the vortex. The study further included a review of what the report describes as a rather extensive experimental program carried out by NASA which specifically involved an effort to reduce the wake hazard of 747 aircraft. The report concludes by stating that the diminution of the wake hazard is still largely an "undeveloped technology". Thus, in spite of the great amount of effort which has gone into examination and solving of this problem, insofar as I am aware nothing thus far made public has been capable of meeting the multiple requirements and restrictions upon such devices which include particularly: structural simplicity; effectiveness for reducing the wing tip vortices; substantial removal from operating position and from the airstream when the aircraft is flying in an area where its wake is immaterial, i.e. at a substantial distance from an airport; and such fail-safe characteristics that in the event of a malfunction of the controlling mechanism, the apparatus will tend to return to its inactive condition.
In the foregoing discussion, it has been assumed throughout that the undesirable aspects of wing tip vortices are manifested solely by disturbances to following aircraft and this is, of course, one of the major undesirable features of such. However, it is also known that wing tip vortices represent a loss in lift effectiveness of a wing and that if the pressure differentials between the lower and upper surfaces of a wing could be maintained undiminished to the extreme end of the wing, that is, prevented from draining or dissipating around the end of the wing, the lifting effectiveness of a given wing could be substantially improved.
While the discussion thus far has been directed toward vortices generated at the wing tips, it has likewise long been recognized that smaller, and in some instances even greater, vortices are generated at the ends of wing flaps. Therefore, it has long been equally desirable to provide means for preventing, or at least inhibiting, such wing flap vortices for the twin purposes of diminishing interferences with following aircraft as above described and for increasing the lift obtainable from a flap of given characteristics, such as length, width and cross-sectional contour.
Accordingly, the objects of the invention include:
1. To provide for aircraft airfoils, particularly wings and/or flaps, a relatively simple means for reducing the tip vortices generated thereby.
2. To provide such means which are inexpensive, reliable and which will be fail-safe.
3. To provide means, as aforesaid, which can be readily effective or ineffective at the will of the pilot.
4. To provide means, as aforesaid, which can be installed into existing aircraft or applied to new aircraft with a minimum of additional expense.
5. To provide means, as aforesaid, which can in a simple manner be visually checked by the pilot to apprise himself of its operability prior to take off or landing, as the case may be.
6. To provide means, as aforesaid, which even when retracted into nonoperating condition will as a secondary function improve the operation of the aircraft.